In communications, in order to correctly receive a desired signal, the desired signal is separated from many other signals that are present on the same medium. This is applicable to wired communication systems and/or wireless communication systems. In the case of wireless communication systems, for example, the task of separating the desired signal from other signals can be a substantial challenge since it might not be known what other signals are present in the air which may interfere with receive circuitry. Further, the transmitter may also interfere with the receive circuitry since the transmitter sits on the same system as the receive circuitry and may operate at the same or a very close frequency to that of the desired receive signal. There are many techniques to isolate a receiver from a transmitter.
As demand for higher bandwidths and better connectivity continues to grow, interest in carrier aggregation has increased. In carrier aggregation, a wireless device may receive the desired information at different frequency bands (or channels) and/or may transmit the information at different frequency bands (or channels).
The requirements for RF filters and multiplexers have become more stringent in light of new communication standards where information channels and frequency bands are closer to each other; new communication devices such as smartphones where the footprint and cost of all components must be very small as more components are needed in support of multiple standards and applications; and co-existing communication systems where multiple communication transmitters and receivers work simultaneously.
Linearity, noise, and power handling requirements might lead to utilization of passive RF filters and multiplexers in many applications. The performance of passive RF filters may be limited by the quality factor (Q) of the components that are used in their realization. The filter selectivity as well as passband requirement may lead to a filter topology and filter order. For a given RF filter topology and order, insertion loss may reduce with the increase of component Q.
Various technologies can be used to realize passive RF filters and duplexers. For instance, capacitors, inductors, or transmission lines can be used to realize passive RF filters and duplexers. Electromagnetic resonators, including waveguide, air cavity, dielectric, and ceramic resonators, can also be used to realize passive filters and duplexers. The quality factor of such components is proportional to their overall physical size. As such, it has been difficult to realize compact low-loss selective passive RF filters and duplexers using electromagnetic components and resonators.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present disclosure as set forth in the remainder of the present application with reference to the drawings.